PROJECT SUMMARY - PROJECT 4: LRRK2 BIOLOGY IN PARKINSON'S DISEASE Parkinson's disease (PD) is a complex neurodegenerative disorder that is both sporadic and familial. Mutations in the leucine-rich repeat kinase 2 (LRRK2) have recently been shown to result in 4% of autosomal dominant familial cases and 1% of sporadic cases worldwide. The clinical and pathological phenotypes of LRRK2 PD patients are similar to classic late-onset PD and LRRK2 knock out animals are resistant to ?- synuclein dopaminergic (DA) neurodegeneration, further emphasizing the potential importance of this gene. This project will address mechanisms of how aberrant kinase activity leads to disease. Our hypothesis is that disease causing LRRK2 GS elicits translational deregulation through pathogenic phosphorylation of s15, leading altered protein expression and neuronal dysfunction and death. Comprehensive understanding of the molecular changes in mRNA translation, the transcriptome and the proteome elicited by LRRK2 GS is required to understand DA vulnerability. There is also an important interaction with ?-synuclein that impacts DA vulnerability but the mechanism is not yet known. Aim 1 to address the ongoing controversy regarding the importance of the increased kinase activity of LRRK2 GS mutation on DA neuronal viability, LRRK2 GS kinase-dead (LRRK2 GS/DA) mice were made. These mice also provide a model to explore the non-kinase actions of LRRK2 that has been lacking from the field. Behavioral, neuroanatomical and neurochemical changes will be monitored over time. The functional interaction between LRRK2 and ?-synuclein toxicity and transmission will be monitored in LRRK2 KO and transgenic lines to determine loss of LRRK2 function is protective and gain of LRRK2 function is toxic. Aim 2 will address the new observation that phosphorylated s15 is a pathogenic target of LRRK2 GS, expression of s15 and phospho-s15 will be monitored in transgenic mice and human postmortem tissue. It will be determined if phosphomimetic s15 is sufficient to elicit neurodegeneration and if phosphodeficient s15 can provide protection from LRRK2 GS neurotoxicity in global and spatially restricted models. These studies will confirm in vivo whether s15 is a pathogenic substrate of LRRK2 GS. Aim 3 will define the specific changes in mRNA translation, the transcriptome and proteome using advanced technologies in genetically engineered mice and human dopaminergic cultures. The use of both mouse and human models allows assessments in the intact brain while investigating acute changes that lead to chronic neurodegeneration in a relevant human system. The unbiased comprehensive datasets will be a valuable resource to all PD investigators. The goal of this project is to identify nodal points in the signal cascade of neurodegeneration that can provide new targets for future development of therapeutic strategies for the treatment of PD.